1. Field of the Invention
This invention relates to an apparatus for inputting location coordinates on an object for image-taking, such as an original or the like, to an image analysis unit, a computer, or the like and, more particularly, to an apparatus for inputting as coordinates, locations indicated by a point indicator within a visual field of an image pickup apparatus.
2. Description of the Prior Art
Coordinate input apparatuses of the type which utilize, for example, a TV camera or an image pickup apparatus such as a camera-type image scanner, have hitherto been put in practical use. Apparatuses of this kind, as compared with other coordinate input apparatuses such as those of using the tablet and the mouse, have the following advantages:
(1) that they do not require any special-type flat bed, or tablet, for inputting coordinates;
(2) that no signal line is required which connects between a device for designating coordinates (i.e., a mouse or the like) and a body; and
(3) that they can perform not only coordinate inputting, but also image data inputting.
As such coordinate input apparatus, for example, one disclosed in Japanese Patent Laid-Open No. 62-47734 is known. This one is a coordinate input apparatus which employs a camera-type image scanner. FIG. 1 is a schematic view showing an outline arrangement of the apparatus, with its mechanical portion shown schematically and its circuit portion shown in the form of a block diagram.
In FIG. 1, reference numeral 1 designates an objective lens disposed in opposed relation to an original 12 as an object for image-taking and between the original 12 and a rotative scanning mirror 2.
The rotative scanning mirror 2, or more concretely a Galvano mirror, is rotated by a drive unit 3.
The drive unit 3 drives the rotative scanning mirror 2 into rotation as above mentioned, causing the latter to change its angle of rotation, said angle of rotation being controlled by a controller 6.
Numeral 4 is a one-dimensional image pickup element using, for example, a CCD (charge coupled device) or the like, which is disposed at a location selected so that rays of light reflected by the rotative scanning mirror 2 will incide thereon. This image pickup element 4 converts light rays incident thereon into electrical signal and outputs the same to a comparator 10.
Numeral 5 is a rotation angle detector of, for example, a rotary encoder or the like for detecting the angle of rotation of the rotative scanning mirror 2, the detected output of the detector 5 being given to the controller 6.
The controller 6 controls the drive unit 3 as above mentioned, and in addition, it controls scanning operation of the image pickup element 4 through an image pickup element driving circuit 11 and receives signals from the rotation angle detector 5 and a comparator 10.
An image signal from the image pickup element 4 is given to a subsampling circuit 9 through the comparator 9 and is subsequently stored in an image memory 7.
The comparator 10 has a certain threshold value preset therein so that if a level of an image signal inputted from the image pickup element 4 exceeds the threshold value, the comparator 10 supplies a predetermined signal to the controller 6. The threshold value set in the comparator 10 is set lower than the value of luminance of an LED as alight emitting element provided at the front end of a point indicator 13 which will be hereinafter described. The comparator 10 does not perform processing with respect to any image signal received from the image pickup element 4 and outputs the same as it is to the subsampling circuit 9.
The subsampling circuit 9 outputs to the image memory 7 image signals received form the image pickup element 4 through the comparator 10 after thinning the number of pixels therein.
The image memory 7 is a page memory for storing image signals inputted from the subsampling circuit 9. Image signals for one page of image which have been stored in the image memory 7 are displayed on a display apparatus 8 such as CRT display. The subsampling circuit 9 is used only in the case where the capacity of the image memory 7 is comparatively small, and it need not be provided if the image memory 7 has a sufficient capacity.
The image pickup element driving circuit 11 supplies to the image pickup element 4 such control signals as reset pulses and transfer clocks to thereby drive and control the image pickup element 4.
The original 12 has an object for image-taking may be a document, a drawing or the like which is written on an ordinary paper sheet, or may be one of any kind unless it includes an object or reflective material having an luminance close to, or higher than the luminance of the LED of the point indicator 13.
As can be seen in FIG. 1, the direction of orientation on the original 12 that corresponds to the direction of element alignment on the image pickup element 4, that is, the direction of main scanning is taken as X direction, and a direction perpendicular to the direction of main scanning, that is, the direction of subscanning, is taken as Y direction.
The point indicator 13, as mentioned above, has an LED as a light emitting element provided at its front end, which is used for indicating a location on the original 12.
Next, the operation is explained. A two-dimensional image of the original 12 and the point indicator 13 is formed by a lens 1 and reflected by the rotative mirror 2 so that it is formed as such on the one-dimensional image pickup element 4. The rotative mirror 2 is tilted to a designated rotational angle by a digital code or analog voltage signal supplied by the controller 6 to the rotative mirror drive unit 3 for designation of the rotational angle, so that any optional main scan portion of the two-dimensional image is formed on the image pickup element 4, which is utilized for feed so that line sequence scanning is carried out as in the case of a TV camera. The rotation angle detector 5 is a mechanical-type or optical-type rotary encoder which detects the rotation angle of the rotative mirror 2 at present moment and outputs a signal thereof, the output being used for calculating the difference between the rotation angle specified by the controller 6 and that at present moment, thereby effecting rotation angle control. The one-dimensional image pickup element 4 driven by the image pickup driving circuit 11 performs image pickup synchronously with subscanning, and image signals from it are stored in the image memory 7 after only necessary portions thereof in the main scanning direction have been selected by the subsampling circuit 9, the stored signals being displayed as an image on the display apparatus 8.
FIG. 2 is a flow chart showing the operational sequence of an original image pickup mode applicable to the prior art arrangement shown in FIG. 1 in which the original 12 is repeatedly scanned all over for image reading, the image being then displayed on the display apparatus 8.
Firstly at step 22, the rotative mirror 2 is set at a predetermined angle (y=0) by the controller 6 and the rotative mirror drive unit 3 so that a leading line of the original 12 can be read. At step 23, the image pickup element 4 is driven by the controller 6 and the image pickup element driving circuit 11, and a one line image in the main scanning direction is taken, image signals thereof being then outputted. At step 24, only necessary portions of the image signals are selected by the subsampling circuit 9, and at step 25 the selected signals are written in the image memory 7 so that they are sequentially displayed on the display apparatus 8. At step 26, calculation is made of an address in the direction of subscanning which corresponds to the next line of the original 12 of which image pickup is required, so that the rotative mirror 2 is set at a corresponding angle (y+.DELTA.y) in the same manner as at step 22.
At step 28, the address in the direction of subscanning and an address of final line the original are compared with each other, and if whole frame reading has been completed, the same procedure as at step 22 is repeated at step 29 for angle resetting (y=0) with respect to the rotative mirror 2. At step 27, each time one line reading and display processing are made as above mentioned, decision is made as to whether an instruction for display mode end has been given by the operator, from input devices not shown, such as key board and mouse or the like, connected to the controller 6, and if the decision is "yes", the display mode is terminated. In the image pickup mode, the comparator 10 does not operate and image signals outputted from the image pickup element 4 are supplied as such to the subsampling circuit 9.
FIG. 3 is a flow chart showing the operational sequence of a coordinate input mode applicable to the prior art arrangement shown in FIG. 1 in which a coordinate is detected of a point on the original 12 which is indicated by the point indicator 13 with a light emitting element mounted thereon.
In FIG. 3, at steps 22, 23, 26, 27, and 29, processing is carried out in the same way as at the corresponding steps in FIG. 2 so that the original 12 and the point indicator 13 are scanned in line sequence for image taking. At step 23, image signals outputted from the image pickup element 4 are supplied to the comparator 10. At step 32, image signals supplied are compared by the comparator 10 with a threshold value of luminance signal level which is preset by the controller 6 or the like and in the case where the signals are higher than the threshold value, the comparator outputs a predetermined signal to the controller 6 and the image pickup element driving circuit 11.
The threshold value of luminance signal level with which image signals are compared is set at such a value as to make it possible to distinguish the original 12 from the light emitting element of the point indicator 13, for example, at a medium value between a maximal value of luminance signals of the original 12 and a luminance signal of the light emitting element of the point indicator 13.
The image pickup element driving circuit 11 gives transfer clock to enable the image pickup element 4 to pick up images and output image signals. The transfer clock is synchronous with image signals supplied to the comparator 10, therefore, by setting transfer clocking at the time of reset pulsing of the image pickup element driving circuit 11 for image pickup of a new line by the image pickup element 4, it is possible to detect an address in the main scanning direction (x address) of image signals supplied to the comparator 10 at a particular point of time. When the comparator outputs a signal, the image pickup element driving circuit 11 which has received the signal retains the count value of the transfer clock, and at step 33 the controller 6 reads the value so retained, whereby an x address of the point indicated by the point indicator 13 can be obtained. As is clear from steps 22, 26 and 29, the rotative mirror drive unit 3 has been given y address by the controller 6 and at step 33 x and y addresses of the designated point are already obtained. Thus the coordinate input mode terminates.
In the comparator 10, a more comparison is made between image signals and the threshold value and no processing is carried out with respect to image signals. Therefore, in the coordinate input mode, image signals are supplied from the comparator 10 to the subsampling circuit 9, whereby coordinate input operation can be made more efficiently.
Constructed as above described, the conventional coordinate input apparatus has a disadvantage that the speed of coordinate detection is determined mainly by the duration taken for image pickup by the image pickup element, so that in the case where a high quality image having a high degree of resolution and high graduation has to be picked up, an image pickup duration of, for example, 3 ms/line is required and in the case where the image is of such a high resolution as 1000 lines in the direction of subscanning, coordinate detection requires 3 seconds at maximum. Such slow rate of response poses a problem in respect of man-machine interface.